Intravenous injection of rat anti-mouse gamma interferon (IFN--y) monoclonal antibody as well as rabbit anti-mouse tumor necrosis factor (TNF) antibody into mice which had received a sublethal infection with Listeria monocytogenes cells resulted in acceleration of listeriosis. Endogenous IFN-'y seemed to be produced early in infection, because suppression of antilisterial resistance was significant when a single injection of anti-IFN--y monoclonal antibody was given on day 0 or day 1 of infection. Production of TNF but not of IFN-y in the bloodstream early in infection was inhibited by administration of anti-IFN-y monoclonal antibody. The suppressive effect of anti-IFN-'y and anti-TNF antibodies on antilisterial resistance was not augmented by simultaneous administration of these antibodies. On the other hand, in the secondary infection, simultaneous administration of anti-IFN--y and anti-TNF antibodies, but not of either of these antibodies alone, into L. monocytogenes-immune mice resulted in high mortality and explosive multiplication of bacterial cells in the spleens and livers. These results suggest that endogenously produced IFN--y and TNF are both essential to the host defense against L. monocytogenes infection and that these cytokines might act by different modes between the primary infection and the secondary infection.

The production and roles of endogenous gamma interferon (IFN-␥), tumor necrosis factor (TNF), and interleukin-6 (IL-6) in both lethal and nonlethal infections of Staphylococcus aureus were investigated in mice. In the case of nonlethal infection, although no bacteria were detected in the bloodstreams, bacteria that colonized and proliferated persistently for 3 weeks were found in the kidneys. All mice given lethal injections died within 7 days, and large numbers of bacteria were detected in the bloodstreams, spleens, and kidneys. The first peaks of IFN-␥, TNF, and IL-6 were observed in the bloodstreams and spleens of the mice with nonlethal and lethal infections within 24 h. Thereafter, in the nonlethal cases, IFN-␥, TNF, and IL-6 peaked again in the spleens and kidneys during the period of maximum growth of bacteria in the kidneys, although only IL-6 was detected in the sera. In contrast, in the case of lethal infection, the titers of IFN-␥ and IL-6 in the sera and TNF in the kidneys peaked before death. Effects of in vivo administration of monoclonal antibodies (MAbs) against IFN-␥ and TNF on the fates of S. aureus-infected mice were studied. In the nonlethal infections, anti-TNF alpha (anti-TNF-␣) MAb-treated mice, but not anti-IFN-␥ MAb-treated mice, died as a result of worsening infection, suggesting that endogenous TNF plays a protective role in host resistance to S. aureus infection. In the mice that received lethal doses, injection of anti-TNF-␣ MAb accelerated death. However, although injection of anti-IFN-␥ MAb inhibited host resistance of the infected mice early in infection, most of the animals survived the lethal infection by injection of anti-IFN-␥ MAb, suggesting that endogenous IFN-␥ plays a detrimental role in S. aureus infection. Thus, this study demonstrated that IFN-␥ and TNF play different roles in S. aureus infection.

Staphylococcus aureus is a common pathogen that causes a wide range of infectious diseases. The function of TLRs, specifically TLR2, during S. aureus infection is still debated. In this study, we investigated the extent to which TLR2 contributes to the host innate response against the bacterial infection using TLR2-deficient mice. Intravenous inoculation with S. aureus resulted in all TLR2-deficient mice dying within 4 d, along with a high bacterial burden in the livers. However, histological examination showed the same degree of macrophage and neutrophil accumulation in the livers of infected TLR2-deficient mice as that in infected wild-type (WT) mice. TLR2-deficient mouse macrophages also showed normal phagocytic activity, although they failed to express CD36 that appeared on the surface of WT mouse cells upon challenge with heat-killed S. aureus. These data indicate that TLR2, as well as CD36, does not directly affect S. aureus clearance and that CD36 expression on macrophages depends on the presence of TLR2. In vivo infection with S. aureus caused significantly elevated production of TNF-α and IL-6 in the livers and blood of TLR2-deficient mice compared with those in WT mice, while the hepatic and serum levels of IL-10 decreased in these mice. In contrast, lower expression of IL-6 and IL-10, but not of TNF-α, at both the gene and protein levels was found in TLR2-deficient mouse macrophages compared to that in WT mouse cells, in response to challenge with heat-killed S. aureus. These findings suggest that the S. aureus-induced pro-inflammatory cytokine response is not dependent on macrophages and that TLR2 deficiency results in decreased IL-10 release by macrophages, which contributes to dysregulated cytokine balance, impaired bacterial clearance, and mouse death. Therefore, TLR2 possesses a protective function during S. aureus infection by regulating pro- and anti-inflammatory cytokine responses.

The production and roles of endogenous interleukin-4 (IL-4) and IL-10 in a sublethal infection with Listeria monocytogenes were studied in normal mice and anti-gamma interferon (IFN-␥) monoclonal antibody (MAb)pretreated mice. In normal mice, the expression of mRNAs for IL-4 and IL-10, which was amplified by reverse transcription-PCR, was induced in the spleens and livers either early or late in infection, although the serum IL-4 and IL-10 were not detectable by enzyme-linked immunosorbent assays. In vivo administration of anti-IL-4 MAb showed no effect on antilisterial resistance, whereas anti-IL-10 MAb partially diminished the defense. In anti-IFN-␥ MAb-pretreated mice, a delay in the bacterial elimination from the spleens and livers was observed and high titers of serum IL-4 and IL-10 were induced late in infection. Production of endogenous IL-4 and IL-10 was suppressed in both CD4 ؉ cell-and CD8 ؉ cell-depleted mice. The suppression of antilisterial resistance in anti-IFN-␥ MAb-pretreated mice was canceled when anti-IL-4 MAb was injected late in infection, whereas anti-IL-10 MAb showed no effect. These results suggest that the host immune responses were polarized into the T-helper 2 phenotype in anti-IFN-␥ MAb-pretreated mice and that inhibition of host resistance against L. monocytogenes by depletion of IFN-␥ might be attributable to IL-4 produced by T cells polarized into the T-helper 2 phenotype as well as the inhibition of the IFN-␥ effects.

Many clinical PET studies have shown that increased 18F-FDG uptake is not specific to malignant tumors. 18F-FDG is also taken up in inflammatory lesions, particularly in granulomatous lesions such as sarcoidosis or active inflammatory processes after chemoradiotherapy, making it difficult to differentiate malignant tumors from benign lesions, and is the main source of falsepositive 18F-FDG PET findings in oncology. These problems may be overcome by multitracer studies using 39-deoxy- 39-18F-fluorothymidine (18F-FLT) or L-11C-methionine. However, 18F-FLT or 11C-methionine uptake in granulomatous lesions remains unclarified. In this study, the potentials of 18F-FLT and 11C-methionine in differentiating malignant tumors from granulomaswere comparedwith 18F-FDGusing experimental ratmodels. Methods: Dual-tracer tissue distribution studies using 18F-FDG and 3H-FLT (groups I and III) or 18F-FDG and 14C-methionine (groups II and IV)were performed on rats bearing both granulomas (Mycobacterium bovis bacillus Calmette-Gue´ rin [BCG]–induced) and hepatomas (KDH-8–induced) (groups I and II) or on rats bearing both turpentine oil–induced inflammation and hepatomas (groups III and IV). One hour after the injection of a mixture of 18F-FDG and 3H-FLT or of 18F-FDG and 14C-methionine, tissues were excised to determine the radioactivities of 18F-FDG, 3H-FLT, and 14C-methionine (differential uptake ratio). Results: Mature epithelioid cell granuloma formation and massive lymphocyte infiltration were observed in the granuloma tissue induced by BCG, histologically similar to sarcoidosis. The granulomas showed high 18F-FDG uptake comparable to that in the hepatomas (group I, 8.18 6 2.40 vs. 9.13 6 1.52, P 5 NS; group II, 8.43 6 1.45 vs. 8.91 6 2.32, P 5 NS). 14C-Methionine uptake in the granuloma was significantly lower than that in the hepatoma (1.31 6 0.22 vs. 2.47 6 0.60, P , 0.01), whereas 3H-FLT uptake in the granuloma was comparable to that in the hepatoma (1.98 6 0.70 vs. 2.30 6 0.67, P 5 NS). Mean uptake of 18F-FDG, 3H-FLT, and 14C-methionine was markedly lower in the turpentine oil–induced inflammation than in the tumor. Conclusion: 14C-Methionine uptake was significantly lower in the granuloma than in the tumor, whereas 18F-FDG and 3H-FLT were not able to differentiate granulomas from tumors. These results suggest that 14C-methionine has the potential to accurately differentiate malignant tumors frombenign lesions, particularly granulomatous lesions, providing a biologic basis for clinical PET studies